Method of treating asbestos ores



Sept. 11, 1928. 1,684,366

S. H. DOLBEAR METHOD OF TREATING ASBESTOS ORES Filed June 5, 1924 2 Sheets-Sheet 1 Inventor 5. H. DOLBEAR METHOD OF TREATING ASBESTOS ORES Sept. 11, 1928 Filed June 5, 1924 2 Sheets-Sheet [nzrenior [ziimfl Patented Sept. 11, 1928 UNITED STATES 1,684,366 PATENT OFFICE.

SAMUEL HOOD DOLBEAR, OF SAN FRANCISCO, CALIFORNIA, ASSIGNOR TO SELECTIVE TREATMENT COMPANY LIMITED, OF MONTREAL. CANADA, A CORPORATION OF QUEBEC.

METHOD OF TREATING ASBESTOS ORES.

Application filed June 3, 1924, Serial No. 717,556, and in Canada November 11, 1922.

This invention primarily relates to methodsasbestos plants is to crush the ore, while in a dry condition, in mills of the so-called cyclone and other high velocity types. Therein, a. very considerable breakage of fibers results, with consequent loss because the commercial value of asbestos, (as quite generally recognized in the art) is largely dependent upon the length of the recovered fibers, the longer fibers being much more valuable than the shorter.

I have discovered, and the present invention is based upon the discovery, that by suitably treating asbestos ore "while submerged in water so as to effect the detachment of asbestos from the associated rocky matter, at the same time avoiding as far as possible the complete separation of the asbestos into its smaller subdivisions or integral fibers,' the destructive action on the fibers may be avoided. In other words, if the asbestos is detached and is partly opened or flutfed, at the same time being given freedom of movement, that the asbestos will move out of contact with the detaching means and may be maintained out of contact therewith until recovered. Freedom of movement of the asbestos away from the detaching instrumentalities is essential to the practice of this invention, as is also the maintenance of the fiber out ofcontact wit-h such ins'trumentalities until recovered. The fiber may be so maintained by agitating the water in which it is submerged.

Any appropriate type of apparatus may be utilized for practising my improved method; but such t s as ball-mills, rod-mills, pebblemills, an other similar types employing a shell or casing and freely movable rolling or grindingelements working therein and capable of being operated with such elements submerged in a fluid, such as water, are well from the associated rocky matter under water,

by my invention, it is important-in fact,

ada tedfor the ur ose and more es eciall the all-mill. p p p I am aware that it has heretofore been proposed to treat .asbestos ore by pulverizing it in a stamp-mill operating in a body of water, the fibers of the massor some of them-floating out of the zone of action of the stamp. In the very nature of this type of apparatus there would be of necessit breakage of the fibers by the impact of the heavy stamp, the weight of which ordinarily runs from 750 to 2250 pounds.

Furthermore, stamp mills, are particularly unsuited to my use as they confine the asbestos in contact with the bed block or mortar, preventing its freedom of movement, and causing the associated rock to cut the fiber. The stamping action also pulverizes the ore.

A desideratum in my invention is to avoid pulverizing the ore, in so far as possible, the ore being treated only sufficiently to detach the fiber from the rock, and to loosen the fiber mass to an extent necesary to give it buoyanc in water. When the rock is pulverized in t e presence of fiber, unnecessary crushing is done, and the pulverized material tends to discolor the fiber. Furthermore, pulverent rock is carried with the fiber, thereby increasing the equipment required for and the cost of subsequent treatment for separation of the two.

My. invention is differentiated from stamp mill action in that, in the mill which I employ-such as the aforementioned ball-mill the fiber is detached and partly opened by the relatively gentle impact of the balls. Where the stamp typeof mill isused, if the stamp, at its lowest point of drop, were submerged in water, the fiber freed by the blow thereof would remain under the stamp and be beaten into short lengths, not only by the impact and pressure of the stamp itself but also by reason of its being subjected to the cutting action of associated pieces of rock. These are serious objections resulting in short length fiber, and which objections, are overcome in a mill such as I contemplate utilizing in the practice of my method.

- Incarrying out the procedure contemplated quite essentialthat the mill be so operated as to house a pool of liquid, such as water, and in which 01 the detached asbestos (resulting from t e action of the detaching elements on the asbestos mass) may readily pass out of contact with such elements, Preferably, in order to achieve the desired results, a portion of the grinding or detaching elements usually employed; in these mills is omittedthat is, a. fewer -number of them than usual are usedso that, when themill is at rest, the water-level therein will be above the plane of the bed of balls. Such a pool, or free-water zone, may also be provided by rotating the mill at a speed sufiicient to cause the mass of the ball-load at one side to be lifted up on one sideof the shell and above the water-level and its opposite side to be con.- siderably submerged below the water-level on the opposite side of the shell. y

I In the accompanying drawings, I have shown the proposed preferred type of apparatus for practisingmy"invention; but in thus illustrating it as a part ofthe disclosure thereof, I wish particularly to say that I am not to be understood as limiting the invention thereto nor in that connection. In these drawings: Figure 1 is a view in perspective of a ball mill adapted for practising my method, a.

portion-of the shell being broken away to show its internahconstructionand its contents;

Fig. 2 is a view in vertical transverse section thereof, on the line 2f 2', Fig. 1

Fig. 3 is .a diagrammatic view in elevation of the shell of the mill of Figs. 1 and 2, show,- ing the normal position .of rolling elements therein when at rest; 1

Fig. 4 is -a similar view but showing the rolling elements in the position theyfoccupy when the mill is rotated at suflicient speed to cause them to be shifted fromtheir'normal position whenat rest; v

Fig. 5 is a view in vertical transverse section, and moreor less diagrammatic, of a modified type of mill;

Fig. 6 is a fragmentary view-in vertical longitudinal section, and more or less dia-v grammatic, of still another-t pe of mill; and

Fig. 7 is a view in verti transverse sec' tion, on the line 7-7, Fig. 6.

Referring to these drawings, and to Figs. 1, 3 and 4 thereof, the reference-character 1 designates a shell or casing forming a component of the mill and having an intake-or .port 2 at one endin the form of a rotating feed-scoop 2-and a discharge or port 3- at the 0 posit e end. The-shell 1s su ported at 4 an 5 for rotation on a horizonta axis, and its driven by a gear 6 which is connected to a suitable prime-mover (not shown).

Within the shell are freely movable grind ing or detaching elements, shownin this instance as balls 7, these beingin number sufficientonly to reach to a level18 under normal conditions. The halls may be of any requiredtype and dimensions for the purposes to he .akcomplished.

A fluid 9-in this instance indicated as water-is contained within the shell and in quantity normally sufficient to reach to a level indicated at 10, and forming a fiberfloating pool 11, this being considerably higher than the level 8 of, but above, the bed of rolling balls, and somewhat above the plane of the bottom of the discharge opening 3. The water is introduced into the shell at the scoop-end, and a certain predetermined quantity thereof (with its liberated fibrous mass) discharges through the opening 3 into a suitable receptacle, such as a fiber-launder 12.

Preferably and as shown, the rocky massgangue-when reduced sufficiently will pass through perforations 13 (in the form of structure shown in Fig. 1) and which perforations' open into a rock-'gangue-launder 16 by which the shell is maintained submerged in the separating liquid. Thus, a peripheraldischarge of the gangue is effected while the bouyant asbestos is discharged ax-' ially 011' the shell, as at 3. In consequence, I

provide for the discharge of the buoyant mass at a level difl'erent and removed from the plane of discharge of the heavier gangue. This eflects a separation of the masses. In

some instances, it may be desirable to locate the perfprations 13 adjacent the discharge end, only, of the mill so,a s to increase the length of time. that the material remains in the mill and subject to the action of the rolling elements. It is to be understood that the number of; these perforations, their distance. from the feed end, etc, may be varied to meet the particular conditions prevailing.

In the structure shown in Fig. 5, the gangue passes through slots 14 formed between equiwhich slots "communicate with "perforations 13 which open into a housing 17 in which the shell '1 1s moun and which housing distantly spaced wearing pl'ates 15,, and" containsa body of liquid in which the shell re-deposited in the field of action of the balls 1n the course of rotationof the shell-,and

eventually reduced to perforation-passing dimensions.

Preferably and as shown, the gangue is removed from the bottom of the tank 16 (Fig.

2) and the housing 17 (Fig. 5) by an elevator gangue lnto a L d, the asbestos ore is introduced into the mill in the usual manner through the scoop 2,

' or by any other convenient means. The ore becomes mixed with the balls, 7, the rocky part of the mass Working downward through the ball-load. As rapidly as the rocky portions of the ore are broken away from the asbestos, the latter becomes partly tiufled or fiherized, whereupon it absorbs water and becomes buoyant. working its way rapidly upward between the balls until it passes into the pool 11 or zone of free water. This pool is kept in a state of agitation by the movement of the balls, such agitation being sufficient to maintain the fiber in suspension and prevent it from sinking into the grinding-zone measured by the field of action of the balls 7. Further to facilitate the discharge of the fiber, it may be desirable to provide irregularities or oli'sets in the liners to cause the balls to cascade, thereby producing an intermittent surge in the mill to cause the fiber to overflow through the discharge by impulse. If the type of ball mill employed be that here shown and having both axial and peripheral discharging means 3 and 13, respectively, (Fig. 1), a concentration is effected and the separation completed by allowing the liber to flow from the mill through the central discharge opening 3, while the heavier, nonbuoyantroecky matter (which has passed downwardly through the ball-load) may be discharged at the periphery through the perforations 13, say, or at some other point below the central or axial discharge means 3. In the event that but one axial discharge means-such as 3is employed, the rocky portion, of the ore is ground to a mesh less than that of the fiber, and the two massesfiber and rock-are then separated by screening. If suflicient separation is not cffected in the mill, this can be secured by passing the material through any appropriate type concentrator, such as that exemplified in United States Patent No. 1,624,184, dated June 28, 1927, of S. H. Dolbear and B. L. Eastman.

In Fig. 4, the apparatus shown is, in general, similar to that illustrated in Figs. 1 to 3; but the normal ball-load-indicated as embracing the balls 7is maintained at a somewhat ditferent position of action; that is to say, the shell 1 is rotated at a suflicient rate of speed in the direction indicated by the arrow to cause the balls to be lifted on the emerging side 18 of the apparatus and lowered at the submerging side 19. In this way, a pool 20, or free-water zone, is provided.

The position or angle of the surface of the ball-load relative to horizontal may be controlled by varying either the spee of rotation of the shell (as in Fig. 4) or the diameter of the shell, or, (to a lesser extent) by changing the size of the balls 7. In a ball-mill of a given diameter and size of balls, the speed necessary to maintain a pool of sutficient depth for the practice of this invention may be readily predetermined by preliminary test.

In Figs. 6 and 7, a somewhat different form of structure is disclosed. In this instance, the shell 24 of the mill is provided with a grate or slotted element 25 provided with a central or axial opening 26 through which the liquid-buoyed fiber 27 passes to the discharge 28, by which it is delivered into the fiberlaunder 29. The gangue 30, reduced by the rolling elements 31, works itself through the slots 25 in the grate and, as the shell rotates, gangue-lifting plates 32 raise the gangue and then drop the ground mass onto a chute 33 (supported independently of the shell, as at 83) by which it is discharged into a ganguelaunder 34.

The operation of so-called rod and pebble mills, so as to practice this invention, is similar to that of the ball-mill; wherefore it is not deemed necessary to illustrate these and, besides, the structural details of these mills are well known to those skilled in the art of hydraulic ore treatment.

In utilizing ball or rod mills such as are available on the market, a pool of water is maintained as described, and the mill operated to effect a detachment of fibers in the manner and under the conditions herein dc scribed. If fibers and gangue matter are discharged together, a separation of the two may be accomplished by utilizing the concentrator of Byron L. Eastman and myself heretofore mentioned herein or by any other suitable means.

Any appropriate predetermined speed of rotation of the mill may be effected so long as the aforementioned water pool within the shell is maintained. In some instances, it may be desirable to rotate the mill at relatively high or abnormal speed; but this may be predetermined in accordance with the requirements. It is important that the pulp shall be relatively thin in contrast to the relatively dense pulp which is usually employed. In this connection, I may state that the results already described may also be accomplished by rotating the mill at usual speed and with the usual ball-load, and effecting the flow of a large volume of water through the mill with sufficient rapidity to carry off unbroken fiber and discharge it from the mill. A thin pulp is desirable, not only because it is then in a condition favorable to agitation but also because thick pulp has a tendency to coat the fiber with fine, crushed rock, which discolors the fiber. The pulp dilution in ordinary ball mill operations varies from 40% to 50% of the weight of the pulp. In milling asbestos ore, however, as contemplated by my invention, a very much larger dilution is preferable, due to the fact that a thick pulp, if produced, discolors the fibers.

It is also found desirable in most cases to discharge relatively coarse hard rock before it is comminuted because only the softer portions of the ore contain fiber and, hence, these are readily comminuted while the harder portions (not containing much if any fiber) should be gotten rid of as soon as possible. In other words, when a given weight of ore say, 100 poundsis placed in a ball mill and ground in water until the fiber ceases to be liberated therefrom, the rocky matter remaining in the mill may constitute as much as 50% of the total ore fed into the mill, and the size of the rocky particles would range up to an inch or more in diameter.

The product resulting from the practice of the hereindescribed method has the following distinctive and distinguishing characteristics, to-wit: It is of natural length; it is stalky in character; it is composed of a multiplicity of pencils; the fiber mass may be somewhat flattened; it is non-pulverent; it is reduced or subdivided along its natural lines of cleavage only; and it has a natural density which will have been changed sufficiently to render the fiber buoyant in water without dividing the mass into its integral fibers.

Where, in the specification, I use the term reducing, or equivalent terms, it is to be understood that these denote the character of milling accomplished, for instance, by the ball milling operation employed by me in which the chief function of the mill is to detach fiber from associated rock and avoiding as far as possible the usual ball milling function of pulverizing the ore, and in contradistinction to a mill crushing action such as is effected by a. stamp mill operation. In other words, as already pointed out, the reduction of the ore in the manner I contemplate results in the separation of the fibers from the gangue in a relatively unbroken state and of normal length, rather than broken and of short length. Moreover, the term grinding, as herein used, contemplates the reduction of the asbestos ore in such a way that the fibers are liberated from the associated harder rtions of the rock, and the separation, uring'the early stages of the operation of the harder, fiber-free particles so that they are rendered inactive to crush or injure the fibers.

Wherel have herein and in the appended claims employed the expression parting, it is intended in its broadest meaning, that is to say, in the sense of separation, division, or dissociation. When thus used, the term may include what in crystallography is technicall known as parting and also what is technically known as cleavage. The expression parting, therefore, is intended to include, broadly, a separation substantially along the longitudinal lines of least cohesion of the fiber.

The inventive-concept involved in the subject-matter of the present case contem lates the treatment of asbestos, as by ball-m1 ing, whereby ore is reduced in a body of liquid until the fiber is detached from the associated rocky matter and divided along the lines of its natural parting only, and the claims herein are directed thereto. In my companion application, Serial N 0; 717,385, filed June 2, 1924, there is disclosed and claimed, broadly and more generically, treatment of asbestos which involves also the reduction of the ore in any appropriate manner (and including ball-milling, if need be) in a body of liquid to produce asbestos in pencil-like form and, then, subsequent treatment to effect a relatively complete concentration of the fiber and other treatment to produce and recover a valuable asbestos product.

avin now described and ascertained the nature 0? my said invention, and the manner in which the same is to be performed, I declare that what I claim is:

1. The method of concentrating asbestos ore which consists in subjectin the ore to under-water treatment, loosening the asbestos and at the same time preserving its natural length, causing the loosened asbestos to pass into a body of water adj aoent the comminuting-zone, and maintaining the loosened asbestos in a state of suspension in said body of water u ntil overflowed.

2. The method of concentrating asbestos ore which consists in subdividing the ore while submerged in water for detaching and dividing the asbestos only along its natural lines of parting and, at the same time, modifying its natural density only sufliciently to render the resultant fiber buoyant, causing the asbestos to become buoyant and to rise into a body of water above the sub-dividing zone, agitating said body of water to keep the buoyant asbestos above the grindingzone, and overflowin the water.

3. The method 0? treating asbestos ore which consists in treating thebre to the action of a. rotating fiber-detaching means operating in a pool of water, malntainin the pool in a state of agitation, detaching t e asbestos, causing the resultant fiberized mass to pass into the pool, and removing the mass from such pool.

4;. The method of treating asbestos ore which consists in subjecting the same to the action of freely-movable rolling elements operating in a mill in which a pool of water is maintained over the rollin elements, and separating the rocky matter From the fibrous portion 0 the ore.

5. The method of treating a bestos ore which consists in subjecting th ore to actionin a ball mill oontaining a body of water normally above and free from the indingzone, causing the "asbestos to pass into sa d body of water, and separating the asbestos from the asoeiated rocky matter.

6. The method of separating asbestos fibre from rock and associated impurities which comprises submerging the mineral in water, subjecting the submerged mineral to a crushing operation to break up the friable elements and separate the asbestos fibres substantially unimpaired as to length, maintaining a circulation of the water and mineral through the crushing means, floating ofi' certain constituents of the mineral, and separating certain of the heavier constituents from the first-mentioned constituents by sedimentation.

7. The method of treating asbestos-ore which includes ball-milling the ore in the presence of an excess of liquid suflicient to effect a division of the fiber along its natural, lengthwise lines of parting only, and to maintain detached fiber in suspension away from the ball-zone.

8. The method of treating asbestos-ore in a ball-mill which includes reducin the mass in a pool of Water in the mill in which there is a ball charge sufiicient to effect division of the fiber along its natural, lengthwise lines of parting only, and supplying the mill with an excess of water.

9. The method of treating asbestos-ore which includes reducin the mass in a ballmill within which is maintained a substantial 001 of water until a division of fiber along its natural, lengthwise lines of parting only is attained.

Signed at New York, N. Y., this 24th day of May, 1924.

SAMUEL H. DOLBEAR. 

